Dopamine, fear & amygdala

w11how

categorising emotions

• complex emotions

• basic emotions

complex emotions

• combinations of basic emotions

• may be socially or culturally learned

• requires cognitive processing

  • not automatically expressed

• e.g regret

basic emotion

• unique characteristics

• developed through evolution

  • fundamental

• reflected in facial expressions

• relatively automatically generated

• e.g fear, sadness

amygdala

• plays a key role in fear

• rats pre amygdala lesion

  • runs away to hide

• rats post lesion

  • no fear response

Learning, emotion & amygdala - fear conditioning

• what we know about amygdala comes from fear conditioning

• first present 2 diff stimuli alone which elicits no response & one that elicits startled response

• train mouse to associated tone w/shock

• tone therefore elicits startled response as shock & tone is paired/associate with each other

extinction

• removing the association of tone w/shock

• if tone occurs without shock over and over

• unlearns the association

Lateral amygdala cells - patterns of firing during fear conditioning (Quirk et al, 1995)

• cells that fire in response to the tone (the conditioned stimulus)

• after training they increase their firing especially in the very early phase after tone delivery

• The plasticity goes away after extinction

role of amygdala in fear conditioning (LeDoux, 1996)

• Amygala lesions block fear learning

• Rats w/amygdala lesions do not learn to associate the noise (CS) with the shock (US) to produce a fear response (CR)

• unable to be conditioned to fear

  

role of amygdala in generation of conscious experience of fear

• is what is the behavioural response to fear

3 patients with bilateral amygdala lesions due to Urbach-Wiethe disease (Feinstein et al. 2013)

• rare disorder in which lesions occur in bilateral (both) amygdala areas

• gave p w/bilateral amygala damage co2 inhalation

  • inhaled CO2 – method of inducing panic

  • Measured rates of panic attacks & subjective fear/panic

• had an elevated panic response

  • All the amygdala patients had panic attacks, only 25% of healthy controls did

• Consistent with earlier suggestions that panic is a false biological alarm, the affective response to CO2 may be part of a protective system triggered by suffocation and acute metabolic distress.

  • they can experience panic

• Amygdala patients and controls who did have panic attacks had similar levels of subjective panic → capable to experience fear

amygdala plays a role in the translation of external threats into a fearful response

• Intact fearful response to carbon dioxide inhalation in patients missing both amygdalae suggests such patients can experience fear

• Suggests amygdala is not necessary for the conscious experience of fear

• perhaps amygdala plays role in translation of external threats into fearful response

conscious or unconscious learning in the amygdala (Bechara et al. 1995)

• studied 3 p – 1 w/amygdala lesion, 1 w/hippocampal lesion, 1 w/damage to both

• Conditioned Stimulus (CS): coloured slide/tone

• Unconditioned Stimulus (US): Boat horn

• Measured Skin Conductance Response (SCR)

• asked P to report explicit knowledge of which CS predicted the US → conscious knowledge

• Measured SCR to loud noises paired with a visual or auditory conditioned stimulus

• double dissociation of conditioning & declarative knowledge relative to amygdala & hippocampus

  • P w/amygdala damage showed impaired SCR to the conditioned stimulus but intact factual learning

    • little skin conductance response

    • can consciously identify

  • P w/hippocampus damage showed normal SCR to the conditioned stimulus but impaired factual learning

    • normal SCR

  • P w/both amygdala & hippocampus damage showed impaired SCR to conditioned stimulus and impaired factual learning

• Amygdala is necessary for implicit learning of threat

• hippocampus is involved in declaritive learning

Role of amygdala in fear summary

• Amygdala necessary for generation of fear response

• Amygdala involved in the translation of threatening stimuli into a behavioural response not in the conscious experience of fear per se

• These data have been influential in the generation of the 2 emotion systems hypothesis

  • Low road: Fast, automatic, immediate responses (amygdala)

  • High road: Slow, conscious experience of emotion (cortex)

LeDoux → 2 emotion systems

• Information about a threatening stimulus reaches the amygdala via two pathways – the high road and low road.

• information takes about 15ms to go down the low road and is fairly crude

• nformation takes about 300 ms to travel down the high road and has a much higher level of detail – the sensory properties of the stimulus are analysed in the visual cortex before travelling to the amygdala

intelligent, goal directed behaviour

• executive function

• working memory

• emotion

• object recognition

• attention

• all contribute to result in goal directed behaviour

• where they are mapped/whether they build on each other